1. Field of the Invention
The present invention relates, generally, to processes and apparati for suppressing the generation of fumes of iron oxides or nitrogen oxides, for example, wherever molten metal, such as steel or iron, is transferred in steelmaking, and, in particular, during the process known as iron beaching. The processes and apparati of the present invention may also be used in non-ferrous metal transfers.
2. Discussion of the Background
In transferring molten metal, such as ferrous metal like steel or iron, during steel production, large quantities of fumes are emitted, particularly red or brown iron oxide fumes resulting from air oxidation of the iron. Of course, the emitted fumes may run afoul of regulations either when outdoors or indoors. This problem can arise in a variety of instances during the production of steel.
For example, molten crude iron or ferromanganese is currently introduced into a casting bed when tapping a blast furnace, in open air, that is, free air access to the molten material is permitted. However, free air access causes several problems. The atmospheric oxygen oxidizes the crude iron or ferromanganese and the resultant oxides rise as pollutants or dust and pollute the surrounding air. In addition, some of the carbon released from crude iron during cooling burns off in atmospheric oxygen resulting in additional emissions.
In order to meet mandated environmental pollution regulations, expensive and energy-intensive dust reduction operations must be performed in casting houses. The high speed air blasts required by these operations cause extensive cooling of the crude iron. This results in a permanent thermodynamic supersaturation of the crude iron with carbon which lead to additional dust emission.
The high air blast speeds and resultant increase in available oxygen causes the carbon in the refractory material in the tapping region to oxidize more quickly, resulting in premature wear. Similarly, the crude iron and ferromanganese are also further oxidized resulting in additional dust pollutants that must be extracted.
Liquid nitrogen has been used in the region of the tapping runner in an attempt to reduce iron oxide pollution by preventing free-air access. However, liquid nitrogen is extremely cold, thus, requiring additional and expensive safety measures for storage and handling. Further, undesired nitriding of the crude iron may reduce the quality of the steel produced.
Fume emission remains problematic wherever molten steel or iron is transferred in steelmaking processes, regardless, of whether it be from container to container or from container to ground or a pit, whether indoors or outdoors. Notably, when iron beaching operations are performed indoors, it is usually necessary to evacuate all mill personnel due to the large amount of red or brown iron oxide fumes produced. Of course, when such operations are effected outside, the iron oxide fumes escape into the atmosphere unabated.
Emissions of a similar nature are present during non-ferrous molten metal transfers, for example, in production of aluminum and copper.
Thus, a need exists, generally, for a method of transferring molten steel, iron or other metals which avoids the above drawbacks. In particular, a need exists for a method of beaching iron which avoids these drawbacks.
Accordingly, it is an object of the present invention to provide a process for transferring molten steel, iron or other metals with reduced fume, dust and/or smoke emissions.
It is also an object of the present invention to provide a means for meeting increasingly strict environmental requirements for emissions stemming from the production of steel and metals generally.
It is, moreover, an object of the present invention to provide an operable carbon dioxide fume suppression system for the ferrous and non-ferrous metals industry.
Accordingly, the above objects and others are provided, in part, by a process for transferring molten metal with reduced fume, dust and/or smoke emission, which entails blanketing the molten metal with, at least, solid carbon dioxide, and allowing the solid carbon dioxide to sublime, thereby restricting free air access to the molten metal, and reducing fume, dust and/or smoke emission therefrom.